The preferred embodiment concerns a method, a computer program and a printing system for trapping of print data.
The preferred embodiment is connected with other disclosures that are described in the German patent applications DE 10 2006 055 587.2, DE 10 2006 055 624.0, DE 10 2006 055 625.9 and DE 10 2006 055 626.7. Their content is herewith incorporated by reference into the present specification.
Color documents or document parts such as, for example, images, color graphics or the like are for the most part described by image data that are subdivided into color separations. This type of data division in turn corresponds to many print output methods or apparatuses that print the image data in color separations on a recording medium, for example in the colors yellow (Y), magenta (M), cyan (C) and black (K) or in black and one or more colors, what are known as highlight color colors or the Océ Custom Tone® colors.
The application develops and distributes corresponding digital electrographic printing systems. For example, they are described in the publication “The World of Printers, Technologies of Océ Printing Systems”, Dr. Gerd Goldmann (Editor), Océ Printing Systems GmbH, Poing, 7th Ed. (2002). Various offset and digital printing technologies are described on pages 249-286, various digital color printing system are described on pages 287-325 and foundations of color printing are described on pages 233-248. Bases of digital image processing are described on pages 209-232. Principles of highlight color printing are described on pages 246-248.
A digital printing system for two-sided monochrome and/or color printing of a recording medium is known from WO 98/39691 A1. A method for preparation of a pixel file in which contiguous areas of the image that are made up of the pixels are determined is known from the international patent application Nr. PCT/EP2004/00700 (publication number WO 2005/001765).
Methods for trapping of image data are known from U.S. Pat. No. 5,581,667, EP-A2-484 890, US 2003/0090689 A1 as well as US 2006/0033959 A1, U.S. Pat. No. 4,931,861, EP-A2-929 189, DE-A1-199 12 511, US 2001/0055130 A1 and EP-A2-833 216.
There is what is known as the passer problem in both digital printing and offset printing. It is thereby that, given a plurality of printing procedures on one sheet of paper, due to mechanical tolerances it cannot be guaranteed that the positioning of the paper is always exactly the same in all printing procedures. The problem occurs in single-color printing when front side and back side are printed separately or given multi-color printing on one side.
Given front and back side printing this problem occurs when, for example, a border is printed on each of the front and back sides and these borders do not exactly lie atop one another, which is noticed when the page is held up to the light.
Given multi-color printing the colors are offset relative to one another. As long as the different colors do not touch, this does not stand out further. If the colors touch, due to the offset, the colors are printed atop one another at the contact line, which leads to an adulteration of the color impression or a white gap (flash) at the contact line.
While the adulteration of the color impression is for the most part still tolerable, the flashes are extremely noticeable, as is shown by the comparison of exactly positioned colors in FIG. 1A and offset positioned colors in FIG. 1B.
To remedy the flash problem it is known to enlarge or, respectively, to spatially over-fill the lighter colors. Although a greater overlap of the colors is therewith obtained, the flashes disappear, as is shown by the comparison of offset positioned colors in FIG. 2A and overlapped colors in FIG. 2B. Given the enlargement of an object care must be taken in the later printing procedure that the overlapping part is printed translucent since otherwise the problem shifts to the edge of the enlarged object.
The method just described that remedies this problem has the name “trapping” (overfilling). Trapping is offered in different products on the market. For example, it is a component of raster image processors (RIPs) of the page description language (PDL) Adobe PostScript Level 3, the software SuperTrap® offered by the company Heidelberger Druckmaschinen AG or the software TrapWise® that is offered by the company Creo.
Trapping can be implemented in two different ways. Trapping can be dealt with at the object level or at the bitmap level.
In electrophotographic high-capacity printing systems the problem of trapping was previously solved at the bitmap level (see, for example, WO 2006/069980 A1), since at the bitmap level the print data can be automatically processed without delay. Corresponding trapping methods can therefore be integrated into an electrophotographic high-capacity printing system without the printing operation hereby being impaired.
However, given the treatment of trapping at the bitmap level the information regarding the objects is missing, whereby the trapping at the bitmap level is in principle significantly less efficient than the trapping at the object level.
The products indicated above that are available on the market (which are components of raster image processors (RIPs) of the page description language (PDL) Adobe PostScript Level 3, the software SuperTrap® offered by the company Heidelberger Druckmaschinen AG or the software TrapWise® that is offered by the company Creo) generate additional trapping objects at the borders of the objects, which trapping objects reduce the effect of the passer problems. These additional trapping objects significantly increase the data volumes of the corresponding print data file. In extreme cases the data volume can even increase tenfold since the number of the individual objects can be multiplied. Given these known solutions the trapping is executed interactively so that an experienced user efficiently controls the generation of the additional trap objects dependent on the document to be trapped. These methods have proven their worth in offset printing, in which a great deal of time is normally available in order to correspondingly process the print document and interactively implement a trapping before the printing procedure.
A method in which a trapping is executed in an electrophotographic printer is known from US 2003/017934 A1. In this method edge lists are produced from the objects and objects that do not correspond to a predetermined shape are divided up into corresponding standard shapes. Information of the objects is thus stored with the edge lists before they are rastered. The trapping itself occurs at the bitmap level, whereby the additional information of the objects (for example in the form of the edge lists) is taken into account as well. The disadvantage of the trapping on the bitmap level, that information regarding the objects is no longer present, is thus somewhat reduced with this method. However, the generation of these edge lists is on the one hand complicated and additionally a plurality of objects are generated from individual objects, which again makes the processing more difficult. Furthermore, the objects so generated are no longer identical with the original objects. Objects with complex shapes cannot be processed or can only be processed in a very limited manner with this method.
A method for trapping of print data present in a print page language (PDL—Page Description Language) arises from U.S. Pat. No. 5,666,543. The print data are hereby initially analyzed and trapping instructions are generated before said print data are supplied to a raster image processor (RIP). The trapping instructions indicate whether the print data comprise text or graphics and whether they should be trapped in the RIP using a shape directory. The shape directory is generated in the analysis of the print data and transmitted to the RIP. The shape directory is a list of the shapes of the objects. The trapping regions or overfills are generated upon rastering in the RIP. This known method corresponds to the method known from US 2003/017934 A1, whereby the shape directory corresponds to the edge list.
The prior art can thus be summarized to the effect that there are trapping methods on the one hand that trap at the object level. However, these methods are not suited to implement the trapping in real time during the printing procedure in a digital electronic printing machine. These methods are primarily provided for offset printing in which the image data are processed with an external raster image processor. On the other hand, it is known to implement trapping in real time in digital electronic printers. However, here the trapping occurs at the bitmap level, whereby limited information regarding the objects is made available to the trapping on the bitmap level by means of edge lists or shape directories.
It was previously assumed that trapping at the object level in a digital printing machine cannot be implemented in real time since a user cannot interactively affect the trapping with regard to the plurality of different rules and the trapping at the object level requires such large-volume files that cannot be processed in real time.
Electrophotographic high-capacity printing systems are often components of digital production printing environments in which the pre- and post-processing of printed media is executed in an automatically controlled manner. In such production environments the document data are transmitted between the individual workstations in the form of document data streams.
Various print data streams and printing systems that are suitable for processing of the most varied print data streams (including AFP and IPDS) are described in the already aforementioned publication “The World of Printers, Technologies of Océ Printing Systems”, Dr. Gerd Goldmann (Editor), Océ Printing Systems GmbH, Point, 7th Ed. (2002), ISBN 3-00-001019-X. In chapter 13 (pages 343 through 361) the print server system Océ PRISMAproduction is described in this regard, for example. This flexible print data server system is, for example, suitable to convert print data from data sources (such as a source computer) into a specific output format (the print data to be received in a specific printer data language such as AFP (Advanced Function Presentation), MO:DCA, PCL (Printer Command Language), PostScript, SPDS (Siemens Print Data Stream), in the Portable Document Format (PDF) developed by the company Adobe Systems Inc. or in the language Line Coded Document Data Stream (LCDS) developed by the company Xerox Corporation) into a specific output format (for example into the Intelligent Printer Data Stream (IPDS) format) and to transfer the data to a print production system in this uniform output format. Various technologies for color printing are described in chapter 10.
In the specification and further development of print data streams the problem sometimes exists that new commands must be inserted into the data stream in order to allow for the further technical developments of computers, printing apparatuses and/or post-processing apparatuses. The establishment of such extensions is for the most part a relatively complicated method in which various industry partners must cooperate in order to match the changes or innovations among one another.
In U.S. Pat. No. 6,097,498 it is described how three new data stream commands (namely WOCC, WOC and END) are to be added to the Intelligent Printer Data Stream (IPDS™).
A further possibility to store additional control data in an AFP data stream is to store data in what are known as object containers (see, for example, the pages 93-95) in the publication Nr. SC31-6802-05.
Further techniques for insertion of new control information into AFP or IPDS data streams are described in WO 03/069548 (originating from the applicant).
How data objects such as text, images, graphics, barcodes and fonts are handled in the data streams AFP and IPDS is described in the IBM publication SC31-6805-05 with the title “Image Object Architecture Reference”. For this what is known as an Object Content Architecture (OCA) is defined in which data structures designated for the respective objects and control parameters or parameters identifying the objects are established; for example, what is known as the Image Object Content Architecture (IOCA) for images, a corresponding GOCA for graphics, a PTOCA for presentation texts etc. The IOCA is described in detail in the aforementioned document. Further IBM documents that are helpful for the understanding of the data streams are cited on pages v through vii of the document.
Details of the document data stream AFP™ are described in the publication Nr. F-544-3884-01, published by the company International Business Machines Corp. (IBM) with the title “AFP Programming Guide and Line Data Reference”. The document data stream AFP was further developed into the document data stream MO:DCA™ which, for example, is described in the IBM publication SC31-6802-06 (January 2004) with the title “Mixed Object Document Content Architecture Reference”. Details of this data stream are also described in U.S. Pat. No. 5,768,488. Specific field definitions of the data stream that contain control data (what are known as “structures fields”) are also explained there.
AFP/MO:DCA data streams are frequently converted into data streams of the Intelligent Printer Data Stream™ (IPDS™) in the course of print production jobs. Such a process is shown in U.S. Pat. No. 5,982,997. Details regarding IPDS data streams are, for example, described in the IBM document Nr. S544-3417-06, “Intelligent Printer Data Stream Reference”, 7th edition (November 2002).
IPDS and AFP data streams normally contain and/or reference what are known as resources that contain data that are required for output of the documents. Via simple referencing, the data of a resource can thereby be used multiple times for one or more print jobs (that in turn comprise a plurality of documents or, respectively, document parts) without having to be transferred multiple times. The quantity of the data to be transferred from one processing unit (for example a host computer generating the documents) to a subsequent processing unit (for example a print server or a printing apparatus) is thereby reduced, in particular when data from a plurality of documents that comprise or require the same data in part are to be transferred. Examples of such resources are character sets (fonts) or forms to be overlaid with documents (overlays). The resources can thereby be contained in the print data stream itself or be transferred separately from this between the participating systems and only be respectively referenced within various documents. It can in particular be provided that the resources are already stored in the further processing apparatus (for example print server or printing apparatus), such that they do not have to be re-transferred with each print job but rather only must be referenced.
Given the presentation of AFP document data, resources that are situated at various points in the AFP document data stream or originate from various sources are merged with the corresponding variable data. The resource data can thereby be integrated into the document data stream as internal resources or be retrieved from libraries as external resources via a resource name. Furthermore, the data are checked for consistency in a parsing process.
In the document “Print Services Facility for OS/390 & z/OS, Introduction”, Version 3, Release 3.0, Nr. G544-5625-03 by the company IBM from March 2002, details are described of how what is known as a line data or MO:DCA document data stream is converted into an Intelligent Printer Data Stream data stream. The software program Print Service Facility (PSF) thereby combines variable document data with resource data into output data that are sent to a printer (as an output apparatus) to administer and control said printer. Software products under the trade name Océ SPS and Océ CIS that exhibit corresponding functions are developed and distributed by the applicant.
A method for secure administration and allocation of resources in the processing of resource-based print jobs is known from US 2005/0024668 A1. A method for processing of resource data in a document data stream is known from WO-A1-2004/0008379.
Methods for color reproduction in offset printing machines are known from Stollnitz, J. et al., “Reproducing Color Images Using Custom Inks”, ACM Proceedings of the 25th annual conference on Computer graphics and interactive techniques, SIGGRAPH '98, ACM Press, July 1998.
The further aforementioned publications or documents and patent applications are herewith incorporated by reference into the present specification, and the methods, systems and measures described there can be applied in connection with the present preferred embodiment.